The present invention relates to liquid level monitoring devices, and more particularly to a liquid level monitoring device for electrically detecting displacement of the surface level of liquid stored in a container.
As one of conventional liquid level monitoring devices of this kind, a fuel gauge has been proposed, which comprises a potentiometer mounted on a portion of a liquid fuel tank and a float member floated on the surface of liquid fuel stored within the tank and slidably in contact with a movable element of the potentiometer. With the fuel gauge, a resistance value of the potentiometer changes in dependence upon displacement of the float member to detect displacement of the surface level of the stored liquid fuel. For the purpose of detecting the liquid fuel surface level, it is required to keep the float member in contact with the movable element of the potentiometer even when the float member is greatly apart from the potentiometer due to decrease of the stored liquid fuel. Additionally, it is required that the weight and capacity of the float member may balance with buoyancy of the liquid fuel to ensure proper changes of the resistance value of the potentiometer. For the above reasons, the fuel gauge may not be constructed in a small size, and the detectable range of the fuel gauge is limited. It has been also observed that erroneous operation of the fuel gauge is caused by defacement in a sliding connection between the float member and the potentiometer.